I agree. We already have a system in place for that. We need to educate people more on how to use it. The flagging works people. You would think a small, mostly intelligent community like sajha should be able to flag posts and remove them from the thread but I have yet to see posts being deleted.
And the ability of the thread creator to delete comments is absurd, I think. Once a thread has been created, it is for everyone to see and respond to. I think the only thing a user should be able to do is to edit his/her post, while still displaying what was edited. Ability to delete post and users not flagging irrelevant post is what is causing sajha to look like a mental asylum sometimes. If you are going to ban, let the people decide who is to be banned. When someone's post is continually being flagged (maybe if 10 unique posts by the user has been flagged by at least 10 different users), ban them. Don't just pick and choose who you want to ban. That would be a better solution I think.

TL;DR - decrease the number from 20 to 10 flags for a post to be deleted. Ban a user if 10 unique posts has been deleted due to excessive flagging.